1. Field of the Invention
The invention relates to a semiconductor device, and more particularly, to a semiconductor device with stress-induced STI or contact plugs.
2. Description of the Prior Art
A conventional MOS transistor generally includes a semiconductor substrate, such as silicon, a source region, a drain region, a channel positioned between the source region and the drain region, and a gate located above the channel. The gate is composed of a gate dielectric layer, a gate conductive layer positioned on the gate dielectric layer, and a plurality of spacers positioned on the sidewalls of the gate conductive layer. Generally, for a given electric field across the channel of a MOS transistor, the amount of current that flows through the channel is directly proportional to a mobility of the carriers in the channel. Therefore, how to improve the carrier mobility so as to increase the speed performance of MOS transistors has become a major topic for study in the semiconductor field.
The formation of SiGe source/drain regions is commonly achieved by epitaxially growing a SiGe layer adjacent to the spacers within the semiconductor substrate after forming the spacer. In this type of MOS transistor, a biaxial tensile strain occurs in the epitaxial silicon layer due to the silicon germanium, which has a larger lattice constant than silicon, and, as a result, the band structure alters, and the carrier mobility increases. This enhances the speed performance of the MOS transistor.
In addition to the application of epitaxial layer, as the semiconductor processes advance, how to increase the driving current for metal oxide semiconductor (MOS) transistors for fabrication processes under 65 nanometer has become an important topic. According to this trend, the utilization of high stress films for increasing the driving current of MOS transistors has become increasingly popular. Currently, the utilization of high stress films to increase the driving current of MOS transistors is divided into two categories: one being a poly stressor formed before the formation of nickel silicides and the other being a contact etch stop layer (CESL) formed after the formation of the nickel silicides.
However, as current approach of either using epitaxial layer or stress films to increase the mobility of carrier in the channel regions of transistor has reached a bottleneck, how to further improve the performance of current device has become an important task.